Method for drying biomass

ABSTRACT

It has been found according to the invention, that a biomass containing an oxidation-sensitive material of value may be dried under particularly mild conditions by a method in which the drying gas is passed over the biomass to be dried in cycle gas mode.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is US national stage of internationalapplication PCT/EP2014/064569, which had an international filing date ofJul. 8, 2014, and which was published in German under PCT Article 21(2)on Jan. 22, 2015. Priority is claimed to European application EP13176661.0, filed on Jul. 16, 2013.

The present invention relates to a method for drying of a biomass undermild conditions, particularly a biomass containing anoxidation-sensitive material of value, and also the biomass obtained bythis method.

The importance of microbial cells for producing materials of value iswell known to those skilled in the art. An example of such materials ofvalue are foodstuff components, in particular lipids, such as, forexample, polyunsaturated fatty acids. A particular role is played in theproduction of such materials of value not only by bacteria and yeasts,but in particular also by other fungi and by algae.

Certain materials of value, in particular polyunsaturated fatty acids(PUFAs), are an important component for the nutrition of humans andanimals. The source originally used for omega-3 fatty acids was mostlyfish. Later, it was discovered that certain microorganisms areheterotrophic producers of omega-3 fatty acids in large amounts, itbeing possible to influence, in an advantageous manner, the fatty acidproduction by selecting specific reaction parameters. Thereafter, theomega-3 fatty acids may be obtained from the cells, or else the cellsmay be employed directly in feedstuffs or foodstuffs in the form ofbiomass.

A problem when using and processing a large number of materials ofvalue, in particular polyunsaturated fatty acids, is the fact that theyare unstable to oxidative degradation: once the material of value isisolated from the cells, the risk of oxidative degradation is greatlyincreased since the protection afforded by the surrounding cell membraneis lost.

However, in accordance with the invention it has been found that adistinct improvement in the properties of the material of value presentcan be achieved even by drying the biomass comprising the material ofvalue under mild conditions and a drying method in which gas is passedover the biomass in cycle gas mode has emerged as particularlyadvantageous.

The object of the present invention, therefore, may be considered asproviding a mild method for drying biomass containing anoxidation-sensitive material of value.

The object according to the invention is achieved by a method for dryinga biomass containing an oxidation-sensitive material of value,characterized in that the method comprises a drying step in which gas ispassed over the biomass in cycle gas mode.

“Cycle gas mode” means that the gas used for the drying is passed overthe biomass in a circulating manner.

In the method step which consists in passing gas over the biomass incycle gas mode, said method is preferably a thermal method. This meansthat the gas used preferably has a temperature above the saturationtemperature of the solvent to be evaporated.

The gas used is preferably air having a reduced oxygen content.

The gas conducted in cycle gas mode preferably has an oxygen content ofless than 20% by weight, preferably less than 15% by weight,particularly from 5 to 13% by weight.

The gas is preferably generated by passing air over a burner and heatingit in this manner. The oxygen content of the air is thereby reduced atthe same time to less than 20% by weight, preferably less than 15% byweight, particularly from 5 to 13% by weight. The gas is constantlyadjusted in the same manner in order to generate a constant gas flowwith reduced oxygen content.

In the drying step, in which the gas in cycle gas mode is used fordrying the biomass, the drying is preferably conducted in a fluidizedbed process. In this drying step, the biomass is particularly preferablyconverted directly into a granulate, such that said step is a spraygranulation process.

A particular advantage of this method consists in that biomass presentin the fermentation broth can be dried and granulated in one step andtherefore only one step is required from the fermentation brothcontaining biomass to the finished product.

A further advantage of this method consists in that the fluidized bedprocess may be operated in continuous and static mode: fermentationbroth containing biomass may be continuously sprayed in and the finishedproduct may be continuously discharged. Preferably, the preparation ofan on-spec product without addition of additives is also possible inthis context.

In this context, in the method according to the invention, the fluidizedbed preferably has a temperature of 45 to 95° C., particularly 45 to 75°C., particularly preferably 45 to 60° C., particularly 50 to 60° C. Theair is correspondingly heated strongly enough that a temperature of 45to 95° C., particularly 45 to 75° C., particularly preferably 45 to 60°C., particularly 50 to 60° C. is reached in the fluidized bed.

As an alternative to the spray granulation method mentioned above, afluidized bed granulation as a fluidized bed process, for example, mayalso be carried out. However, it is generally required in this case thatthe fermentation broth containing biomass is initially converted into asolid product, by spray-drying for example.

Fluidized bed systems which may be used in methods according to theinvention are obtainable, for example, from Glatt GmbH, Germany.

The biomass to be employed in accordance with the invention comprisescells but may also contain other components. The biomass preferablytakes the form of the product of a fermentative culturing process.Accordingly, the biomass may comprise not only the cells but alsocomponents of the fermentation medium. These components may take theform of, in particular, salts, antifoam agents and unreacted carbonsource and/or nitrogen source. The cell content in this biomass amountsto preferably at least 70% by weight, preferably at least 75% by weight.If appropriate, the cell content in the biomass may be increased bysuitable wash steps to, for example, at least 80 or at least 90% byweight before carrying out the drying process. However, the biomassobtained from the fermentation process may also be employed directly inthe drying process.

Cells present in the biomass may take the form of cells which alreadynaturally produce materials of value, preferably lipids, in particularPUFAs, but may also take the form of cells which have been made capableof producing lipids, in particular PUFAs, by means of suitable geneticengineering methods. In this context, the production may be autotrophic,mixotrophic or heterotrophic.

The biomass preferably comprises cells which produce lipids, inparticular PUFAs, heterotrophically. According to the invention, thecells are preferably algae, fungi, in particular yeasts, or protists;however, cells from oil-producing plants are, for instance, alsosuitable. The cells are especially preferably microbial algae or fungi.

Cells of oil-producing plants which are particularly suitable are theseeds of soybeans, flax, oil seed rape, maize, cotton, safflower andsunflower.

Suitable cells of oil-producing yeasts are, in particular, strains ofYarrowia, Candida, Rhodotorula, Rhodosporidium, Cryptococcus,Trichosporon and Lipomyces.

The biomass according to the invention preferably comprises cells fromthe taxon Labyrinthulomycetes (Labyrinthulea, slime nets), in particularthose from the family Thraustochytriaceae. The family of theThraustochytriaceae includes the genera Althomia, Aplanochytrium, Elnia,Japonochytrium, Schizochytrium, Thraustochytrium and Ulkenia. Thebiomass particularly preferably comprises cells from the generaThraustochytrium, or Schizochytrium, above all those from the genusSchizochytrium.

The term “Schizochytrium” according to the invention also includes thenew genera Aurantiochytrium and Oblongichytrium which have recentlyemerged through the reclassification of the genus Schizochytrium. Aparticularly preferred species of schizochytria used in accordance withthe invention is Schizochytrium limacinum (now: Aurantiochytriumlimacinum), particularly from the Schizochytrium limacinum SR21 strain.

The oxidation-sensitive material of value is preferably anoxidation-sensitive lipid, particularly an unsaturated fatty acid,particularly preferably a polyunsaturated fatty acid (PUFA) orhighly-unsaturated fatty acid (HUFA).

The cells present in the biomass are preferably distinguished by thefact that they contain at least 20% by weight, preferably at least 30%by weight, in particular at least 40% by weight, of material of value,preferably of lipids, especially preferably of PUFAs, in each case basedon cell dry matter.

In a preferred embodiment, the majority of the lipids in this case ispresent in the form of triglycerides, with preferably at least 50% byweight, in particular at least 75% by weight and, in an especiallypreferred embodiment, at least 90% by weight of the lipids present inthe cell being present in the form of triglycerides.

Furthermore, the lipids present in the cell preferably comprisepolyunsaturated fatty acids (PUFAs), with preferably at least 10% byweight, in particular at least 20% by weight, especially preferably 20to 60% by weight, in particular 20 to 40% by weight, of the fatty acidspresent in the cell being PUFAs.

According to the invention, polyunsaturated fatty acids (PUFAs) areunderstood to mean fatty acids having at least two, particularly atleast three, C—C double bonds. According to the invention,highly-unsaturated fatty acids (HUFAs) are preferred among the PUFAs.According to the invention, HUFAs are understood to mean fatty acidshaving at least four C—C double bonds.

The PUFAs may be present in the cell in free form or in bound form.Examples of the presence in bound form are phospholipids and esters ofthe PUFAs, in particular monoacyl-, diacyl- and triacylglycerides. In apreferred embodiment, the majority of the PUFAs is present in the formof triglycerides, where preferably at least 50% by weight, in particularat least 75% by weight and, in an especially preferred embodiment, atleast 90% by weight of the PUFAs present in the cell are present in theform of triglycerides.

Preferred PUFAs are omega-3 fatty acids and omega-6 fatty acids, withomega-3 fatty acids being especially preferred. Preferred omega-3 fattyacids in this context are eicosapentaenoic acid (EPA, 20:5ω-3), inparticular (5Z,8Z,11Z,14Z,17Z)-eicosa-5,8,11,14,17-pentaenoic acid, anddocosahexaenoic acid (DHA, 22:6ω-3), in particular(4Z,7Z,10Z,13Z,16Z,19Z)-docosa-4,7,10,13,16,19-hexaenoic acid, withdocosahexaenoic acid being especially preferred.

Processes for production of biomass, particularly biomass which containscells comprising lipids, particularly PUFAs, particularly from the orderThraustochytriales, are described extensively in the prior art. As arule, the production takes place by cells being cultured in a fermenterin the presence of a carbon source and of a nitrogen source. In thiscontext, biomass densities of more than 100 grams per litre andproduction rates of more than 0.5 gram of lipid per litre per hour maybe attained (WO 01/54510). The process is preferably carried out in whatis known as a fed-batch process, i.e. the carbon and nitrogen sourcesare fed in incrementally during the fermentation. When the desiredbiomass has been obtained, lipid production may be induced by variousmeasures, for example by limiting the nitrogen source, the carbon sourceor the oxygen content or combinations of these (WO 01/54510).

Preferably, the cells are fermented in a medium with low salinity, inparticular so as to avoid corrosion. This can be achieved by employingchlorine-free sodium salts as the sodium source instead of sodiumchloride, such as, for example, sodium sulphate, sodium carbonate,sodium hydrogen carbonate or soda ash. Preferably, chloride is employedin the fermentation in amounts of less than 3 g/l, in particular lessthan 500 mg/l, especially preferably less than 100 mg/l.

Suitable carbon sources are both alcoholic and non-alcoholic carbonsources. Examples of alcoholic carbon sources are methanol, ethanol andisopropanol. Examples of non-alcoholic carbon sources are fructose,glucose, sucrose, molasses, starch and corn syrup.

Suitable as nitrogen source are both inorganic and organic nitrogensources. Examples of inorganic nitrogen sources are nitrates andammonium salts, in particular ammonium sulphate and ammonium hydroxide.Examples of organic nitrogen sources are amino acids, in particularglutamate, and urea.

In addition, inorganic or organic phosphorus compounds and/or knowngrowth-stimulating substances such as, for example, yeast extract orcorn steep liquor, may also be added so as to have a positive effect onthe fermentation.

The cells are preferably fermented at a pH of 5 to 11, in particular 6to 10, and preferably at a temperature of at least 20° C., in particular20 to 40° C., especially preferably at least 30° C. A typicalfermentation process takes up to approximately 100 hours.

After the fermentation has ended, the biomass is harvested. Afterharvesting the biomass or even optionally shortly before harvesting thebiomass, the cells are preferably pasteurised in order to kill the cellsand to inactivate enzymes which might promote lipid degradation. Thepasteurisation is preferably effected by heating the biomass to atemperature of 50 to 121° C. for a period of 5 to 60 minutes.

Likewise, after harvesting the biomass or even optionally shortly beforeharvesting the biomass, antioxidants are preferably added in order toprotect the material of value present in the biomass from oxidativedegradation. Preferred antioxidants in this context are BHT, BHA, TBHA,ethoxyquin, beta-carotene, vitamin E and vitamin C. The antioxidant, ifused, is preferably added in an amount of 0.01 to 2% by weight.

In a first step, a portion of the fermentation medium may now already beseparated from the biomass and the solid fraction can thus be increased.This may be carried out in particular by centrifugation, filtration,particularly ultrafiltration or microfiltration, decanting and/orsolvent evaporation. In this case the solvent is preferably evaporatedusing a rotary evaporator, a thin film evaporator or a falling-filmevaporator in a single stage or multistage process. A useful alternativeto solvent evaporation is, for example, reverse osmosis forconcentrating the fermentation broth.

In this first optional but preferred step, the fermentation medium ispreferably concentrated to a solid content of at least 10 or 15% byweight, preferably of at least 20 or 25% by weight, particularly 10 to50 or 15 to 45% by weight, particularly preferably 20 to 40% or 25 to40% by weight.

This means that the biomass to be dried in a method according to theinvention is preferably present in the form of a suspension having thesolid fraction stated above, where the liquid component of thesuspension is preferably a fermentation broth or concentratedfermentation broth.

After concentration or partial removal of the fermentation broth, thebiomass is dried in accordance with the invention by passing preferablyheated gas over the biomass or biomass suspension in cycle gas mode.

Alternatively, the biomass may also be dried by a cycle gas processdirectly after harvesting, particularly if the fermentation brothobtained already has a high solid content, preferably as stated above.

As already mentioned, air in which the oxygen concentration has beenreduced, preferably as stated above, is preferably used for drying.

The suspension is preferably dried to a residual moisture content of atmost 10% by weight, particularly 0 to 10% by weight, particularlypreferably at most 8% by weight, particularly 0.5 to 8% by weight, aboveall at most 6 or 5% by weight, particularly 1 to 6 or 1 to 5% by weight,by drying the biomass in cycle gas mode.

As already stated above, the drying of the biomass according to theinvention is preferably carried out in a fluidized bed granulationprocess. The fermentation broth comprising biomass is to this endsprayed into the fluidized bed granulation drying system. A granulationdrying system which can preferably be used according to the invention isshown schematically in FIG. 1 of EP 0809940.

The drying gas is introduced from below into the fluidized bedgranulation drying system. The majority of the moisture in the injectedfermentation broth evaporates and the granulate formed is maintainedsuspended by the gas flow of the drying gas. In this state, theparticles are separated from one another and in this manner are freelyaccessible to the droplets when further liquid is sprayed into the bed.Also in this state, the heat and mass transfer between the solidparticles and the gas flow is intensive. Product particles of thedesired size are continuously removed from the fluidized bed in aclassical offtake.

The fluidized bed or the bed of particles, which must be present at thebeginning of the fluidized bed granulation drying process, preferablyconsists of dried particles of the biomass used for drying, for example,from a batch of a previous run. It is, however, equally possible to useanother material as fluidized bed for initiating the fluidized bedgranulation drying process.

A particular advantage of the fluidized bed granulation process is thatthe process can be operated continuously and the fermentation brothcomprising biomass can be converted to a product having the desiredparticle size in one step.

The particles produced additionally have an excellent consistency andhave very good bulk properties and flow characteristics due to theiressentially round shape. The particles also have a low residual moisturecontent.

A free-flowing, fine-grained or coarse-grained product, preferably agranulate, is preferably obtained by the drying process according to theinvention. A product having the desired particle size can optionally beobtained from the granulate by sieving or dust separation.

Providing a free-flowing fine-grained powder was obtained, this canoptionally be converted into a coarse-grained, free-flowing and largelydust-free product, which can be stored, by suitable compacting orgranulating processes.

Conventional organic or inorganic auxiliaries or supports such asstarch, gelatine, cellulose derivatives or similar substances, which aretypically used in food processing or feed processing as binding agents,gelling agents or thickeners, may optionally be used for the granulationor compaction.

“Free-flowing” according to the invention is understood to mean a powderthat can flow out unhindered from a series of glass efflux vesselshaving different size outflow openings, at least from a vessel having a5 millimeter opening (Klein: Seifen, Öle, Fette, Wachse 94, 12 (1968)).

“Fine-grained” according to the invention is understood to mean a powderhaving a predominant fraction (>50%) of particle sizes of 20 to 500micrometers in diameter.

“Coarse-grained” according to the invention is understood to mean apowder having a predominant fraction (>50%) of particle sizes of 500 to2500 micrometers in diameter.

“Dust-free” according to the invention is understood to mean a powderthat contains only a low fraction (<5%) of particle sizes below 100micrometers.

Grain or particle size is preferably determined according to theinvention by laser diffraction spectrometric methods. The methods to beused are described in the textbook “Teilchengrößenmessung in derLaborpraxis” by R. H. Müller and R. Schuhmann, WissenschaftlicheVerlagsgesellschaft Stuttgart (1996) and also in the text book“Introduction to Particle Technology” by M. Rhodes, published by Wiley &Sons (1998). Inasmuch as various methods can be used, the first-citedusable method from the text book of R. H. Müller and R. Schuhmann forthe determination of particle size is preferred.

The products obtained according to the invention preferably have afraction of at least 80% by weight, particularly at least 90% by weight,particularly preferably at least 95% by weight, above all at least 97%by weight, of particles having a particle size of 100 to 3500micrometers, preferably 1000 to 3000 micrometers, above all 1500 to 2500micrometers.

Owing to the preparation process, preferably at least 50% by weight,particularly at least 70% by weight, particularly preferably at least90% by weight, above all essentially all particles are formedessentially spherical in shape. Especially the formation of essentiallyspherical particles accounts for the excellent bulk properties and flowcharacteristics of the product according to the invention.

“Formed essentially spherical in shape” is understood to mean, inaccordance with the invention, that the diameter of a particle isessentially uniform in all spatial directions. “Essentially uniform” isunderstood to mean here that the variance of the diameter of a particlein any two spatial directions is at most 20%, preferably at most 15%,particularly at most 10%, particularly preferably at most 5%.

The fraction of dust, i.e. particles having a particle size of less than100 micrometers, is preferably at most 1% by weight, particularlypreferably at most 0.5% by weight.

The bulk density of the product according to the invention is preferablyfrom 400 to 800 kg/m³, particularly preferably from 450 to 700 kg/m³.

An object of the invention, therefore, is also a particulate biomasswhich may be obtained by a method according to the invention and also aparticulate biomass which comprises oxidation-sensitive material ofvalue, having the properties mentioned above, in particular having theproperties mentioned above with respect to particle size and particledistribution. In terms of the preferred nature of the biomass and thepreferred material of value present, reference is made to thatpreviously discussed.

The biomass obtained according to the invention may be used in variousways. After drying of the biomass in accordance with the invention, thedried biomass is preferably stored or packed. The biomass cansubsequently be used, for example, to manufacture foodstuff or feedstuffor to isolate the material of value from the biomass.

A feedstuff or foodstuff comprising a particulate biomass according tothe invention is a further object of the present invention.

A further object of the present invention, therefore, is also a methodfor isolating the material of value from a particulate compositionaccording to the invention.

In order to increase the bioavailability in the feedstuff or foodstuffto be produced and/or to facilitate the isolation of the material ofvalue present in the biomass, the particulate biomass is preferablysubjected to a cell-disruption process. The material of value mayalternatively also be isolated directly from the particulate biomasswithout said prior disruption.

A cell suspension is preferably prepared, based on the dried biomass,before carrying out the cell-disruption method. For this purpose, thedried biomass is mixed with water or an aqueous solution in order toprepare a cell suspension having a moisture content of preferably atleast 30% by weight, particularly 30 to 90% by weight, particularlypreferably 40 to 80% by weight, above all 50 to 75% by weight.

The cells may be subsequently disrupted using the cell disruptionmethods known to those skilled in the art, such as by using a screwextruder, a beater mill, an air-nozzle mill or by applying an elevatedpressure, for example by what is known as the French Press method.Alternatively or additionally, the cells may be disrupted by using cellwall digesting enzymes.

The cell disruption is preferably carried out in accordance with theinvention by using a rotor-stator system. The rotor-stator system isbased on a stationary part, referred to as the stator, and a rotatingpart, the rotor. The rotor typically has a circumferential speed of atleast 5 m/s, for example 10 to 30 m/s, and the gap between rotor andstator may be for example 0.1-0.5 mm. To disrupt the cells, the cellsuspension is placed into the gap between stator and rotor. The cellsare subjected to a shear stress in the gap and, additionally,turbulences are caused. These two factors bring about the disruption ofthe cells. In a preferred embodiment, the suspension is prepared in therotor-stator system using a solid mixing attachment. A solid mixingattachment in this context is understood to mean a device which allowsthe separate introduction of solid on the one hand and water or aqueoussolution on the other hand into the rotor-stator system. The suspensionis therefore prepared only during the cell disruption or immediatelybefore the cell disruption by mixing in the solid mixing attachment. Inaccordance with the invention, it has been found that, by using such asolid mixing attachment, suspensions with very high solid contents maybe subjected to the cell disruption process, which is particularlyadvantageous with respect to the subsequent processing. Suspensions,used when a solid mixing attachment is used in the rotor-stator system,preferably have a solid content of 20-50% by weight, particularlypreferably of 30-50% by weight.

If an aqueous solution is used to prepare the cell suspension, it maycomprise in particular other foodstuff components—such as vitamins orsalts.

According to the invention, the energy input into the cells,particularly when using a rotor-stator system, is preferably at most 50kWh per tonne of suspension, particularly at most 40, 35 or 30 kWh pertonne of suspension, particularly preferably at most 25, 20 or 15 kWhper tonne of suspension. Preferred ranges in this context are energyinputs of 0.1-50 kWh per tonne of suspension, particularly 0.3-45 kWh,particularly preferably 0.5-40 kWh, particularly 0.8-35 kWh, above all1-30 kWh, particularly 1.5-25 kWh, 2-20 kWh or 3-15 kWh, in each caseper tonne of suspension.

The “cell disruption rate” of the process according to the invention ispreferably at least 50%, particularly preferably at least 60, 70 or 80%,above all at least 85, 90 or 95%. The “cell disruption rate” isunderstood to mean the number of disrupted cells, after the end of thecell disruption process, as a ratio to the total number of cells. Thecell disruption rate may be determined visually, for example, using amicroscope, as the ratio of the number of disrupted cells relative tothe total number of cells.

To stabilize the materials of value, particularly lipids, againstoxidative degradation, the cell suspension used for the cell disruptionmay additionally comprise antioxidants. Preferred antioxidants in thiscontext are BHT, BHA, TBHA, ethoxyquin, beta-carotene, vitamin E andvitamin C. The antioxidant, if used, is preferably present in an amountof 0.01 to 2% by weight. In a preferred embodiment, the antioxidants inthis case are already added to the fermentation medium after completionof the fermentation.

The material of value may be isolated from the biomass either proceedingfrom the intact dried biomass or proceeding from the disrupted biomass.

The material of value may be isolated from the disrupted biomass, forexample, by a simple mechanical removal of the cell debris, for exampleby decanting, filtration or centrifugation.

The material of value can otherwise be isolated both from the intact andalso from the disrupted biomass, for example, by solvent extraction.Once the material of value has been separated off, accordingly, thesolvent can be removed, for example by applying reduced pressure.Alternatively, the material of value can be isolated, for example, bysupercritical fluid extraction.

The solvents used may be the solvents known to those skilled in the art,for example, chloroform, ether, hexane, methylene chloride or methanol.The oil may also be separated, for example, by using a different oil forextracting the oil according to the invention.

The oil may subsequently be subjected to chemical or physical refining.Refining may comprise degumming, bleaching, filtering, deodorizingand/or polishing of the crude oil. Individual oil components may thenoptionally be isolated.

Both the intact and the disrupted biomass and also the materials ofvalue isolated from the biomass may be used to prepare a foodstuff orfeedstuff, in which the biomass or the material of value are preferablymixed with other foodstuff or feedstuff ingredients and are subsequentlyprocessed to form the foodstuff or feedstuff.

The mixture of biomass and other foodstuff or feedstuff ingredients areprocessed in a preferred embodiment by an extrusion process, in order toproduce portions of foodstuff or feedstuff ready for sale.Alternatively, a pelleting method may also be used.

A screw or twin-screw extruder is preferably employed in the extrusionprocess. The extrusion process is preferably carried out at atemperature of 80-220° C., particularly 100-190° C., a pressure of 10-40Bar, and a shaft rotational speed of 100-1000 rpm, particularly 300-700rpm. The residence time of the mixture introduced is preferably 5-30seconds, in particular 10-20 seconds.

In a mode of the extrusion process which is preferred in accordance withthe invention, the process comprises a compacting step and a compressionstep.

It is preferred to intimately mix the components with each other beforecarrying out the extrusion process. This is preferably carried out in adrum equipped with vanes. In this mixing step, a preferred embodimentincludes the injection of steam, in particular so as to bring about theswelling of the starch which is preferably present.

Before being mixed with the disrupted cells, the further foodstuff orfeedstuff ingredients are preferably comminuted—if required—so as toensure that a homogeneous mixture is obtained in the mixing step. Thecomminuting of the further foodstuff or feedstuff ingredients may becarried out, for example, using a hammer mill.

A process which is preferred in accordance with the invention forpreparing foodstuff or feedstuff therefore comprises the followingsteps:

a) preparing a biomass, preferably by fermenting fungi or microalgae,which produce a material of value, preferably a lipid, particularlypreferably omega-3 fatty acids;

b) drying of the biomass obtained under mild conditions, wherein thedrying under mild conditions comprises passing over gas in cycle gasmode and where the oxygen content of the gas is preferably less than 20%by weight, in particular less than 15% by weight, particularlypreferably 5 to 13% by weight and the previously described spraygranulation process is preferably used for the drying;

c) mixing the biomass and/or materials of value isolated therefrom,optionally after carrying out a prior cell disruption process, withother foodstuff or feedstuff ingredients;

d) preparing the final product by a compacting or extrusion process.

A very particularly preferred method in accordance with the inventionfor preparing a foodstuff or feedstuff comprises in this case thefollowing steps:

a) preparing a biomass, preferably by fermenting fungi or microalgae,above all slime nets, which produce a material of value, preferably alipid, particularly preferably omega-3 fatty acids;

b) drying under mild conditions the biomass obtained to a moisturecontent of preferably less than 15% by weight, preferably less than 10%by weight, in particular 1-9% by weight, particularly preferably lessthan 5% by weight, particularly 1-4.5% by weight, wherein the dryingunder mild conditions comprises passing over gas in cycle gas mode andwherein the oxygen content of the gas in this case is preferably lessthan 20% by weight, in particular less than 15% by weight, particularlypreferably 5 to 13% by, weight and the previously described spraygranulation process is preferably used for the drying;

c) converting the biomass into a cell suspension having a moisturecontent of at least 30% by weight, preferably 30 to 90% by weight,particularly preferably 40 to 80% by weight, in particular 50 to 75% byweight;

d) disrupting the cells, preferably employing an energy input of no morethan 50 kWh per tonne of suspension, preferably 0.1-50 kWh, particularly0.3-45 kWh, particularly preferably 0.5-40 kWh, particularly 0.8-35 kWh,above all 1-30 kWh, particularly 1.5-25 kWh, 2-20 kWh or 3-15 kWh, ineach case per tonne of suspension, preferably using a rotor-statorsystem;

e) mixing the disrupted cells and/or materials of value isolatedtherefrom with other foodstuff or feedstuff ingredients;

f) preparing the final product by means of a compacting or extrusionprocess.

Preferred methods for preparing a foodstuff or feedstuff according tothe invention are preferably characterized in that the energy input tothe biomass is no higher than 50 kWh per tonne of suspension in anymethod step. The energy input to the biomass is preferably at most 40 or35 kWh, particularly at most 30 or 25 kWh, particularly preferably 20 or15 kWh, in each case per tonne of suspension. This additionally ensuresthat the material of value present is adversely affected as little aspossible.

The disrupted cells preferably account for 0.5-20% by weight,particularly 1-10% by weight, preferably 2-8% by weight of the foodstuffor feedstuff or of the composition used for preparing the foodstuff orfeedstuff.

The foodstuff or feedstuff is preferably a product for use inaquaculture or a foodstuff or feedstuff for use in poultry production,pig production or cattle production. The feedstuff may also take theform of a feedstuff which is employed for growing small organisms whichmay be employed as feedstuff in aquaculture. The small organisms maytake the form of, for example, nematodes, crustaceans or rotifers. Thefeedstuff is preferably present in the form of flakes, spheres ortablets. A feedstuff obtainable by extrusion has a moisture content ofpreferably less than 5% by weight, especially preferably 0.2 to 4% byweight.

The other foodstuff or feedstuff ingredients are preferably selectedfrom protein-containing, carbohydrate-containing,nucleic-acid-containing and lipid-soluble components and, ifappropriate, further fat-containing components and furthermore fromamong other additives such as minerals, vitamins, pigments and aminoacids. Besides, structurants may also be present, besides nutrients, forexample so as to improve the texture or the appearance of the feedstuff.Furthermore, it is also possible to employ, for example, binders so asto influence the consistency of the feedstuff. A component which ispreferably employed and which constitutes both a nutrient and astructurant is starch.

The following examples may be employed as protein-containing componentwhich additionally contains fats: fish meal, krill meal, bivalve meal,squid meal or shrimp shells. As an alternative, fish oil may also beemployed as a fat-containing component. A vegetable oil may also beemployed as a fat-containing component, in particular oil from soybeans,rapeseed, sunflower kernels and flax seed. An example of acarbohydrate-containing component which may be employed is wheat meal,sunflower meal, soya meal or cereal gluten.

The total oil content in the feedstuff—including the oil from theoil-containing cells—amounts preferably to 15-50% by weight.

The feedstuff for use in aquaculture is preferably used for breedingfinfish and crustaceans which are preferably intended for humannutrition. These include, in particular, carp, tilapia, catfish, tuna,salmon, trout, barramundi, bream, perch, cod, shrimp, lobster, crabs,prawns and crayfish. It is especially preferably a feedstuff for salmonfarming. Preferred types of salmon in this context are the Atlanticsalmon, red salmon, masu salmon, king salmon, keta salmon, coho salmon,Danube salmon, Pacific salmon and pink salmon.

Alternatively, it may also be a feedstuff intended for farming fishwhich are subsequently processed to give fish meal or fish oil. Thesefish are preferably herring, pollack, menhaden, anchovies, caplin orcod. The fish meal or fish oil thus obtained, in turn, can be used inaquaculture for farming edible fish or crustaceans.

Aquaculture may take place in ponds, tanks, basins or else in segregatedareas in the sea or in lakes, in particular in cages or net pens.Aquaculture may be used for farming the finished edible fish, but alsofor farming fry which are subsequently released so as to restock thewild fish stocks.

In salmon farming, the fish are preferably first grown into smolts infreshwater tanks or artificial watercourses and then grown on in cagesor net pens which float in the sea and which are preferably anchored inbays or fjords.

Accordingly, a further object of the present invention is also a methodfor farming animals, in particular finfish or crustaceans, preferablysalmon, in which a feedstuff according to the invention is employed. Afurther object of the present invention is additionally an animal, inparticular a finfish or shellfish, which is obtainable by such a methodaccording to the invention.

The present invention further provides methods for obtaining anoxidation-sensitive material of value from a biomass comprising a dryingstep in accordance with the invention.

The invention claimed is:
 1. A method for drying a microbial biomasscontaining an oxidation-sensitive material of value, comprising a dryingstep in which drying gas is passed over the biomass in cycle gas mode,wherein the drying gas has an oxygen content of 5 to 13% by weight andthe oxidation-sensitive material is an unsaturated fatty acid; whereinthe drying gas is produced by a method consisting of heating air.
 2. Themethod of claim 1, wherein the oxidation-sensitive material of value isan omega-3 fatty acid or an omega-6 fatty acid.
 3. The method of claim1, wherein the drying step is a fluidized bed process in which thefluidized bed has a temperature of 45 to 95° C.
 4. The method of claim1, wherein the biomass is both dried and granulated in one step.
 5. Themethod of claim 3, wherein the fluidized bed process is operated incontinuous and static mode, fermentation broth containing biomass iscontinuously sprayed in and the finished product is continuouslydischarged.
 6. The method of claim 1, wherein the biomass comprisescells from the taxon Labyrinthulomycetes.
 7. The method of claim 1,wherein the biomass comprises cells from the family Thraustochytriaceae.8. The method of claim 1, wherein the biomass comprises cells from thegenera Thraustochytrium, Schizochytrium or Ulkenia.
 9. The method ofclaim 1, wherein the biomass used in the drying step is in the form offermentation broth with a solid content of 20 to 40% by weight.